1. Field of the Invention
The present invention relates to an improved rechargeable lithium battery with a specific anode formed of lithium. More particularly, the present invention relates to an improved rechargeable lithium battery which exhibits an excellent current collecting performance and is free of occurrence of a dendrite (or a branched tree-like protrusion) of lithium upon repetition of charging and discharging.
2. Related Background Art
In recent years, heating of the earth because of the so-called greenhouse effect due to an increase of atmospheric CO.sub.2 has been predicted
In the case of the steam-power generation, the amount of a fossil fuel represented by coal or petroleum to be consumed for power generation in order to comply with a societal demand for increased power supply has been continuously increased and along with this, the amount of exhaust fumes from the steam-power generation plants has been continuously increased accordingly to raise the content of gases to cause a greenhouse effect such as carbon dioxide gas in the air. This results in providing an earth-warming phenomenon. In order to prevent said earth-warming phenomenon from further developing, there is a practice of prohibiting to establishment of a steam-power generation plant in some countries.
Under these circumstances, there has been made a proposal of conducting so-called load leveling in order to effectively utilize the power generator, wherein rechargeable batteries are installed at general houses and a surplus power unused in the night. That is, a so-called dump power, is stored in said rechargeable batteries and the power thus stored is supplied in the daytime when the power demand is increased, whereby the power generator is leveled in terms of the load therefor.
By the way, there is an increased societal demand for developing a lightweight rechargeable battery with a high energy density for an electric vehicle which does not exhaust any air polluting substance such as CO.sub.x, NO.sub.x, SO.sub.x, hydrocarbon, and the like. Other than this demand, there are increased societal demands for developing a miniature, lightweight, high performance rechargeable battery usable as a power source for potable instruments such as small personal computers, word processors, video cameras, and pocket telephones.
As such rechargeable battery, there has been proposed a rocking chair type lithium ion rechargeable battery in which a lithium intercalation compound is used as an cathode active material and carbon is used as a anode active material. However, as of the present time, there has not been realized a practical usable lithium ion rechargeable battery having a sufficiently high energy density, which is considered could be attained by using a metallic lithium as the anode active material.
The public attention has now focused on the rechargeable lithium battery in which metallic lithium is used as an anode, but as of the present time, there has not yet been attained a practically usable, high capacity rechargeable lithium battery with an improved energy density Particularly, as for the known rechargeable lithium battery, there is a problem in that lithium is often deposited in a dendritic state (that is, in the form of a dendrite) on the negative electrode (or the anode) upon the charging operation, wherein such dendritic deposition of lithium metal results in causing internal-shorts or self-discharge. As one of the reasons why such practically usable, high capacity rechargeable lithium battery as above described has not been realized, in the absence of means capable of preventing the occurrence of the above dendritic lithium deposition has not been developed
Now, as above described, once the above lithium dendrite is formed, the dendrite is liable to gradually grow upon the charging, resulting in causing internal-shorts between the anode and the cathode. When the anode suffers from internal-shorts with the cathode as above described, the energy possessed by the battery is shortly consumed at the short-circuited portion to entail problems such that the battery is heated or the solvent of the electrolyte is decomposed by virtue of heat to generate gas, resulting in raising the inner pressure of the battery. These problems result in damaging the battery or/and shortening the lifetime of the battery.
There has been proposed a manner of using a lithium alloy such as lithium-aluminum alloy as the anode for a rechargeable lithium battery in order to suppress the reactivity of the lithium so that a lithium dendrite is hardly generated. This manner is effective in preventing the generation of the lithium dendrite but is not effective in attaining a rechargeable lithium battery having a high energy density and which is long enough in cycle life.
Particularly, Japanese Unexamined Patent Publication No. 13264/1988 (hereinafter referred to as document 1), No. 47381/1993 (hereinafter referred to as document 2) or No. 190171/1993 (hereinafter referred to as document 3) discloses a non-aqueous series rechargeable battery in which the anode is constituted by a lithium alloy. However, any of the rechargeable batteries disclosed in these documents 1 to 3 is problematic in that as the charging and discharging are repeated, the anode is repeatedly expanded and shrunk to often suffer from a crack, wherein the rechargeable battery eventually becomes poor in current collecting performance.
Additionally, Japanese Unexamined Patent Publication No. 114057/1988 (hereinafter referred to as document 4) discloses a non-aqueous series rechargeable battery in which the anode is constituted by a basic constituent comprising a sintered body of a mixture composed of fibrous aluminum and fibrous metal incapable of being alloyed with lithium and a negative material comprising a lithium-aluminum alloy. However, the rechargeable battery disclosed in the document 4 is problematic in that as the charging and discharging are alternately repeated over a long period of time, expansion and shrinkage are liable to repeatedly occur at the fibrous aluminum to deteriorate its adhesion with the fibrous metal incapable of being alloyed with lithium or to cause a crack at the interface between the fibrous aluminum and the fibrous metal, wherein the rechargeable battery eventually becomes poor in current collecting performance
Further, Japanese Unexamined Patent Publication No. 234585/1993 (hereinafter referred to as document 5) discloses a non-aqueous series rechargeable battery in which the anode is constituted by a member made of lithium metal having powdery metal (which hardly forms an intermetallic compound with said lithium metal) uniformly deposited on the surface thereof. As for this rechargeable battery, the document 5 describes that it is slight in terms of the generation of a dendrite, high in charging and discharging efficiencies, and long in cycle life. However, the rechargeable battery disclosed in the document 5 is still problematic in that as the charging and discharging are alternately repeated, expansion and shrinkage are liable to repeatedly occur at the lithium metal member and as a result, the powdery metal deposited on the lithium metal member is often removed or a crack often occurs at the lithium metal member, resulting in making it difficult to sufficiently prevent the occurrence of a dendrite and also in making the rechargeable battery to be poor in current collecting performance.
Further in addition, Journal of Applied Electrochemistry, 22, 620-627 (1992) (hereinafter referred to as document 6) discloses a rechargeable lithium battery in which the anode (or the negative electrode) is constituted by an aluminum foil having a surface applied with etching treatment. However, the rechargeable lithium battery disclosed in the document 6 is problematic in that when the charging and discharging cycle is repeated as many as that practically conducted for the ordinary rechargeable battery, problems are liable to arise in that as the charging and discharging are alternately repeated, the aluminum foil is repeatedly expanded and shrunk to suffer from a crack, resulting in causing a reduction in the current collecting performance, wherein the growth of a dendrite is liable to occur.
Hence, any one of the rechargeable batteries disclosed in the documents 1 to 6 is still accompanied by some problems required to be solved.
Accordingly, there is an increased demand for provision of an improved rechargeable lithium battery which is high in energy density and long enough in cycle life.